The present invention relates to an oscillation compensating apparatus for a vortex flow meter.
One approach to the measurement of a flow rate of a fluid is, as well known in the art, a vortex flow meter which includes a vortex shedding member disposed in a fluid passage or conduit. With this type of flow meter, an instantaneous flow rate of a fluid flowing through the conduit is measured in terms of frequency of oscillations of the vortex shedding member which results from the Karman vortex street, or vortex train, shed in the conduit downstream of the vortex shedding member.
A problem has existed in the vortex flow meter in that a sensor thereof sensitive to the oscillations of the vortex shedding member, or shedder, picks up not only oscillations due to the vortex train but various kinds of externally derived oscillations, thereby making accurate flow rate measurement difficult. Sources of the externally derived oscillations include a pump for compressing the fluid and a damper which is mechanically opened and closed. Implementations for solving this problem are disclosed in Japanese Utility Model Laid-Open Publication Nos. 57-19465/1982 and 57-28370/1982 for example, which are characterized by the use of two oscillation sensors. The output of one of the two sensors is employed to automatically control the triggering level of a Schmitt trigger or, alternatively, the outputs of both sensors are combined with each other. However, such implementations are not fully acceptable from the viewpoint of their applicable flow rate range, because the two sensors located at different positions which make noise signals picked up thereby different in waveform or because strict adjustment is required in positioning the sensors.